Many known roof drain assemblies comprise a roof drain insert member and a clamp ring member to overlie and be clamped onto a top flange of the insert member. Typically, internal lugs are provided on both the clamp ring member and the top flange which extend radially inwardly into the tubular drain. This has the disadvantage that the lugs can restrict flow of water. To prevent excessive interference with water flow, the lugs are located closely adjacent inside walls of the tubular drain. To accomplish this, however, for each different size tubular drain, a different size clamp ring is required. Provision of internal lugs makes it very difficult to mould drain insert members in that two piece moulds can not be used and more complex mould constructions are required. A further disadvantage of the internal lugs is that their use results in concentration of forces on the lugs increasing the likelyhood of failure and possible leakage.
Screws to secure typical clamp ring members onto flanges of the drain insert members are located flush with or below the upper surface of the ring members. This has the disadvantage that the holes into which the screws are to be placed or the screws themselves are frequently hidden and covered with tar, asphalt or other sealants applied to the roof about the roof drain insert. This can be a substantial inconvenience and loss of time during installation.